The present invention relates generally to ablation devices that use electromagnetic energy to ablate internal biological tissues. More particularly, the present invention relates to an improved electrode arrangement for sensing electrical activity of internal biological tissues.
Medical ablation devices have been around for some time. For example, ablation catheters utilizing electromagnetic energy, in both the RF and microwave frequency ranges, have been introduced and employed to various degrees to ablate biological tissues. One common application is to ablate myocardium tissues to treat a variety of cardiac arrhythmias. By way of example, representative microwave ablation catheters are described in the U.S. Pat. No. 4,641,649 to Walinsky; U.S. Pat. No. 5,246,438 to Langberg; and U.S. Pat. No. 5,405,346 to Grundy, et al., each of which is incorporated herein by reference.
Most existing microwave ablation catheters contemplate the use of antennas that produce a peripherally extending field that surrounds the catheter. That is, the electromagnetic energy generated by the antenna is propagated laterally to the sides of the catheter relatively uniformly about the antenna region of catheter. Although such catheter designs work well for a number of applications, in many applications it would be desirable to provide a more directional field that concentrates most of the electromagnetic energy generated by the antenna in a predetermined direction.
There have been some efforts to provide catheters and/or other ablation instruments with more directional fields. By way of example, U.S. Pat. No. 5,800,494 to Campbell, et al. and co-pending U.S. application Ser. No. 09/333,747 to Berube (Oct. 23, 1999) describe a number of antenna designs that generate generally forward firing fields. Additionally, U.S. Pat. No. 5,314,466 to Stem, et al, and co-pending U.S. application Ser. No. 09/178,066 to Berube, et al. (Jun. 14, 1999) describe antenna designs that generate generally side firing fields. Although such designs work well, there are continuing efforts to improve antenna designs to provide ablation instruments with specific directional components, such as in a lateral direction to one side of the catheter.
During positioning and/or use of the ablation catheter, it is often desirable to monitor certain electrophysiological properties of the heart. To facilitate such electrophysiological monitoring, electrodes are often positioned near the distal end of the catheter. Typically, such electrodes take the form of annular metallic rings. However, in some implementations, the annular rings have been replaced with electrode bands with multiple electrodes per band. By way of example, U.S. Pat. No. 5,788,692 to Campbell, et al. describes a mapping catheter with split electrode bands. Although the existing electrode designs work well, there are continuing efforts to improve their functionality.
To achieve the foregoing and other objects of the invention, an improved electrode arrangement for use in medical instruments is described. The described electrode arrangement is capable of sensing electrical activity of biological tissues inside the body of a patient in substantially one direction. The electrode arrangement is also capable of being positioned in small spaces on the medical instrument. The electrode arrangement includes a pair of elongated wire electrodes, which are positioned on one side of the medical instrument. The pair of wire electrodes are positioned side by side and arranged to be parallel to one another. The pair of electrodes are also spaced apart and electrically isolated from each other. The electrode arrangement also includes a pair of electrode wires that are electrically coupled to an associated wire electrode.
The described electrode structure can be used in a wide variety of medical instruments including catheters and various other surgical instruments. By way of example, they can be used in ablation devices, drug delivery devices, specimen retrieval devices, and the like.
In some preferred embodiments, the electrode arrangement is used to determine the position of medical instrument with respect to adjacent biological tissues. For example, the electrode arrangement is used to measure electrical activity of the tissue in the heart (e.g., cardiac), the brain (e.g., cerebral), the prostate, the stomach, the intestines, the liver and the like
In some preferred embodiments, the electrode arrangement is used in medical devices with components that work in substantially one direction, such as laterally to one side of the medical device. In these embodiments, the electrode arrangement is positioned to sense electrical activity in a direction that coincides with the directional component of the medical device. In a related embodiment, the electrode arrangement is used in an ablation device that produces a directional electromagnetic field for ablating biological tissues.
In some embodiments, the wire electrodes are arranged to extend side by side longitudinally relative to the medical device and have centerlines that are radially spaced from one another between about 15 and about 90 degrees, and more particularly less than 45 degrees. In other embodiments, the wire electrodes are disposed on the medical device proximate a working member, such as the antenna of a microwave ablation catheter. In such a case, the wire electrodes may be positioned proximate the distal or proximal end of the antenna or may be positioned between the distal and proximal ends of the antenna.
In some embodiments, the electrode wires are formed from a good electrical conductor wire and coupled to a pair of surface mount resistors. In other embodiments, the electrode wires are positioned such that they are electrically isolated from electrical components inside the medical device.